Mass spectrometry is one of the simpler spectrometric concepts wherein molecules of a sample are ionised, then the ions are separated generally according to their mass to charge ratio in a mass analyser and then detected. Mass analysers of many types are available, such as magnetic field, combined electric and magnetic field, quadrupole, ion-cyclotron resonance, quadrupole ion storage trap and time of flight analysers. Of these, time of flight mass spectrometry (TOFMS) provides high sensitivity and is able to measure extended (virtually limitless) mass ranges. It is therefore ideally suited to the analysis of bio and synthetic polymers. TOFMS also has an advantage over other methods of mass analysis in that the complete mass spectrum is obtained from every ionization event. However TOFMS instruments are large and require very high vacuum conditions (10−6 Torr) because of the length of the field free drift region (about 0.5 to 1 m long) that is required in which ions of different masses are separated. A reflectron (an ion mirror) has been included at the end of the drift region to reflect ions back through the drift region and this has allowed improved mass resolution. However the problems remain that TOFMS instruments are large, very high vacuum instruments.
Another high sensitivity mass analyser that provides excellent resolution is one that uses the ion-cyclotron resonance (ICR) phenomenon, for example as in a Fourier Transform Mass Spectrometer (FTMS). In FTMS, ions are allowed to circulate within an ion trap in defined orbits over extended periods of time. An ac input signal is applied which modifies the ion orbits depending upon mass/charge ratios of the ions. Ions are detected by their generation of an “image current” as they pass an electrode. The time-domain signal that is produced is then Fourier transformed into a frequency domain signal and then into the corresponding mass spectrum. FTMS instruments, however, are expensive.
The discussion herein of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the matters referred to were part of the common general knowledge in the art in Australia as at the priority date of any of the claims.
An object of the present invention is to provide a mass spectrometer and method therefor having high sensitivity, high resolution and a capability of measuring extended mass ranges, and in which the above described problems of TOFMS and FTMS are reduced.